1. Field of the Invention
The invention is derived from consideration of risers in offshore floating structures, related more particularly to cylinder-stem assemblies for risers, and is generally applicable to the interfacing of any structure that can move within its supporting structure.
2. General Background
Cylinders such as buoyancy cans that function as tensioning devices for top-tensioned production and export risers have been used with conventional and truss-type spars and deep draft caisson vessels that serve as floating, deep-water, hydrocarbon drilling and/or production platforms. Buoyancy can tensioning could be used to tension risers for tension leg platforms (TLPs) but have not seen such use so far as is known. Prior buoyancy cans with stems have had four, six, or eight wear strips that contact guides supported in the hull and/or space frame (truss) of the floating platform. Such guides may contact wear strips not only on the buoyancy can but also on the upper stem and possibly lower stem that extend respectively above and below the buoyancy cans. Buoyancy can guides connected to the structure of such floating platforms have been either nominally round (toroidal) to contact the buoyancy can wear strips at any location or have been plates or other flat surfaces that are positioned nominally tangent to the exterior surface of the round (cylindrical) buoyancy can.  Flat plate guides have been monolithically affixed to the structure of such floating platforms or have been supported with a cushion of compliant material such as an elastomeric material to soften impact loads caused by the relative movement between the buoyancy can and the floating platform. Alternatively, the compliant guide may have an interference fit so there is constantly a force of contact that may be sufficient to prevent separation of the wear strip and guide, thus eliminating impact forces (if it is sufficient) or at least rendering them much less frequent and severe.